Papers by Author: Kin P. Cheung

Abstract: In this paper we report TDDB results on SiO₂/SiC MOS capacitors fabricated in a matured production environment. A key feature is the absence of early failure out of over 600 capacitors tested. The observed field accelerations and activation energies are higher than what is reported on SiO₂/Si of similar oxide thickness. The great improvement in oxide reliability and the deviation from typical SiO₂/SiC observations are explained by the quality of the oxide in this study.

Abstract: In this paper we report an unexpected improvement in the SiC DMOSFET transistor characteristics after a long temperature treatment at 150 C. The evolution of the device characteristics during a TDDB stress is compared to that after an elevated temperature treatment. The improvement in characteristics after storage at high temperature is believed to be due to instabilities caused by the quality of the SiO₂/SiC interface and its large density of defects.

Abstract: The quality of the SiC/SiO₂ interface is critical to the stability and performance of MOS-based SiC power devices. Charge pumping is a flexible interface characterization technique. In this work, a significant portion of the total traps are found to be located in the near-interface oxide using frequency-dependent charge pumping. Oxide trap tunneling mechanisms are discussed, and trap profile as a function of depth is calculated. The trap density is shown to increase exponentially as it gets closer to the interface.

Abstract: Low channel mobility is one of the biggest challenges to commercializing SiC MOSFETs. Accurate mobility measurement is essential for understanding the mechanisms that lead to low mobility. The most widely used effective mobility measurements overestimate the inversion charge for devices that have high level of defects. Mobility measured by the Hall effect is more accurate; however the conventional Hall mobility measurement is tedious. In this work, we demonstrate a wafer-level Hall measurement technique, which is simple and convenient to implement. With this method, extensive study of the mobility degradation is possible.

Abstract: Reliability of the gate oxide on SiC is a pressing concern for deploying SiC MOS-based devices in real systems. While good projected oxide reliability was obtained recently under highly accelerated test conditions, indication that such projection may not be valid at lower operating fields was also reported. In this work, results from long-term TDDB stress (over 7 months) at 6 MV/cm and 300 °C on 4H-SiC MOS capacitors is reported. We confirm that lifetime projection from high-field data continues to be valid and no change in field acceleration factor is observed. The discrepancy between our results and the early prediction of poor reliability is examined.

Abstract: SiC MOSFET, as power device, can be expected to operate with high drain and high gate voltages, possibly leading to hot-carrier effect. However, hot-carrier degradation in a SiC MOSFET is difficult to detect because the as fabricated devices contain high level of defects. We report, for the first time, evidence of hot-carrier effect in 4H-SiC MOSFET. The result suggests that hot hole from impact ionization trapped in the oxide is the cause of the channel hot-carrier effect.